Controllable voltage converter system having a high switching speed

Abstract

Two identical variable voltage source include respective capacitors serially interconnected across a series combination of a capacitive load and a fixed voltage source. Each variable source further includes a commutation reactor having two windings electromagnetically coupled and connected to each other, and two thyristors connected across the capacitor through one of the reactor windings to invert a voltage across the capacitor from its positive to its negative polarity and vice versa respectively. Either one of two low impedance DC sources charges the capacitor through a mating thyristor and the other reactor winding.

What is claimed is: 
     
       1. A voltage converter system for a capacitive load comprising: a fixed voltage source connected serially to said capacitive load, and at least one variable voltage source connected across a series combination of said capacitive load and fixed voltage source, said variable voltage source including a capacitance operatively coupled to said capacitive load, a reactor having a pair of windings electromagnetically coupled and connected to each other, first circuit means formed of said capacitance, one of said reactor windings and a first switch means interconnected serially to one another, said first switch means being controlled to invert the polarity of a voltage charged on said capacitance, and a second circuit means including a low impedance DC source, second switch means, the other of said reactor windings and said capacitance interconnected serially to one another, said second circuit means either charging said capacitance from said low impedance DC means in the steady state or responding to a reaction applied thereto through the other winding of said reactor upon inverting the polarity of the voltage across said capacitance, to bias reversely said second switch means so as to thereby stop the charging of said capacitance, wherein the voltage across said capacitive load is stepwise controlled in response to the control effected by said first switch means. 
     
     
       2. A voltage converter system as claimed in claim 1, wherein each of said first and second switch means is formed of a thyristor. 
     
     
       3. A voltage converter system as claimed in claim 1 wherein each of said first and second switch means is formed of a reverse conducting thyristor and a semiconductor diode connected serially thereto.